Ferrofluid seal apparatuses are well known for providing exclusion and pressure-type seals about shafts. Such ferrofluid seal apparatuses may be composed of a single, dual or multiple-stage ferrofluid seals and conventionally comprise a source of magnetic flux, such as a permanent magnet, and one, two or more pole-piece elements in a magnetic-flux relationship with the source of magnetic flux, with the one end of the pole piece extending into a close, noncontacting relationship with the surface of the shaft, to form a radial gap, and ferrofluid retained in the radial gap, to form an O-ring-type ferrofluid seal about the surface of the shaft. Ferrofluid exclusion seals, using a single or a dual pole piece; that is, with little pressure capacity, are conventionally employed as exclusion seals for computer-disc-drive shafts. The annular permanent magnet and the pole pieces are usually secured within a housing and the housing is used to provide a means of attachment for the seal, when it is mounted onto or about a shaft or spindle, and wherein the ferrofluid seal is used to exclude airborne particulate and vapor contaminants from entering a sealed area. It is also common practice to install the ferrofluid seal directly to the spindle, without the use of seal housing; that is, to employ the spindle housing, itself, as a ferrofluid seal housing.
Such ferrofluid exclusion seal apparatuses are conventionally assembled and secured by a variety of techniques, such as employing a chemical technique, such as the use of adhesives, and mechanical techniques, such as the use of a retaining ring, to secure the permanent magnet and the one, two or multiple pole pieces and magnets within a housing. Both of the present prior-art methods of assembly are not wholly satisfactory. Chemical adhesive assembly results in a rather fragile ferrofluid seal apparatus and is not completely dependable in terms of sealing. Mechanical techniques, employing a retaining ring, while mechanically strong, do not provide adequate airtight sealing. Mechanical techniques also typically require additional sealing components, such as an O-ring, which further adds to the cost and complexity, and also makes the ferrofluid seal assembly undesirably large, which precludes its use in certain defined areas. Further, both the chemical and mechanical methods tend to be labor-intensive and, therefore, somewhat costly, while both methods use materials or techniques that render the ferrofluid seal assembly inherently contaminated with particles, adhesive residues, oils or other undesirable elements. This further increases the cost of assembly, by requiring subsequent cleaning operations, in order for the ferrofluid seal assembly to be accepted for its intended use, such as for sealing computer-disc drives or rotating optics enclosures.
Therefore, a ferrofluid seal apparatus which avoids the disadvantages of the prior art and the method of assembling such seal apparatuses, to provide an improved, less labor-intensive and lower-cost ferrofluid exclusion seal, is most desirable.